The spectrograph uses a 1024x1024 Aladdin 3 Insb array. The
saturation well-depth is about 8000 Data Numbers (DN) for
the default bias of 0.4V, the gain 13.0 electrons/DN, the
dark current 0.2 electrons/sec over long integrations and the
readnoise 50 e RMS per read. With 32 non-destructive reads (NDRs)
(minimum itime about 17 sec with default SlowCnts of 20 - see below)
the readnoise is reduced to about 12 e RMS. The number of NDRs
is automatically selected by the software. Shorter itimes
reduce the number of NDRs. If efficiency is a concern then the number
of NDRs can be set manually (see C). The SlowCnts parameter allows the array
to be readout at different speeds. With 20 SlowCnts the minimum
ITIME is 0.51sec, with 3 SlowCnts the minimum itime is 0.18sec.
The penalty for faster read out is higher readnoise although
in practice the reason for increasing the readout rate is because
of higher background where readnoise is not an issue. At 0.4V bias
the array is linear to about 5 percent up to 4000DN. FOR GOOD
LINEARITY CORRECTION (in Spextool) AND TO SAFELY AVOID SATURATION,
IT IS STRONGLY RECOMMENDED THAT COUNTS BE KEPT BELOW ABOUT 4000 DN.

The SpeX guider uses a 512x512 Aladdin 2 Insb array. The saturation
well-depth is about 5000 Data Numbers (DN) for the default bias of
0.4V, the gain 13 electrons/DN, the dark current 1.5 electrons/sec
over long integrations and the readnoise 65 e RMS per read. Up to
2500DN the device is linear to about a 10 percent. The full guider
array (512x512 pixels) minimum ITIME is 0.24sec using the
default value of 12 SlowCnts. With 3 SlowCnts the minimum ITIME
is 0.12sec. However, at this speed fixed pattern noise becomes
noticeable. Subarrays can be used to reduce the ITIME further
For example, a 256x256 subarray has a minimum ITIME of 0.04sec
using 3 SlowCnts. For this particular device, increasing the
bias does not usefully increase the well-depth. TO SAFELY AVOID
SAFELY AVOID SATURATION, IT IS STRONGLY RECOMMENDED THAT COUNTS
COUNTS BE KEPT BELOW ABOUT 2000 DN (although IR guiding works well
on saturated images).
Observers should note that the guider array is currently not corrected for
linearity. To get photometry to 1% level the object and standard need to be
exposed to approximately the same well depth, otherwise photometry can be off
by up to 10%. Work is underway to include linearity correction (ask). Flat fielding
can be done on the sky or dome. For wavelengths longer than 2.5 microns flat fielding
does not work but dithering images can achieve a few percent photometry.

=0.2 SlowCnt=9 (NDRs automatically set to 1).
real time=0.2+(1x0.2)=0.4 per coadd
efficiency = 50%
The efficiency in this mode can be increased by decreasing
SlowCnts to the acceptable minimum of 3 for the guider which
has a minimum ITIME of 0.12sec, but at the cost of increased
column structure (noise):
ITIME=0.2 sec, NDRs=1
real time=0.2+(1x0.12)=0.32 per coadd
efficiency= 63%

Data is usually saved to the 70 GB scratch disk on stefan eg.
/scrs1/bigdog/your_name/date, where bigdog indicates spectrograph
data. The path is setup by clicking AUTOSAVE ON in the
bigdog xuiwindow and then typing in the path. Similarly
for the IR guider/imager e.g. /scrs1/guidedog/your_name/date,
where guidedog indicates guider data. These data are owned by
bigdog and guidedog, irrespective of the path name, and so you
must open a bigdog or guidedog window to erase data. For better
efficiency movie mode data are usually saved to the local disks
on bigdog or guidedog eg. /data/your_name/bigdog/date and
/data/your_name/guidedog/date. The local /data disk have much
smaller capacities and so the space must be managed carefully.

Note that the header parameter DIVISOR is the product of NDRs
and COADDS. Fits files must be divided by ITIME x DIVISOR to
get DN/sec. The SpeX Data Viewer (DV) is set by default to divide by
the DIVISOR (under SETUP) but check to make sure. Data reduction
packages such as IRAF do not automatically divide by ITIME X DIVISOR
to get DN/sec, this must be done explicitly. Observers frequently
make this mistake and find that their counts (DN/sec) are too large
by a factor of the DIVISOR. Spextool automatically accounts for the
DIVISOR.